1. Field of the Invention
This invention relates to a high efficiency space conditioning process and apparatus for heating and cooling utilizing an absorption cycle in the nature of absorption heat pumps for heating and cooling. This invention provides a process and apparatus having higher Coefficient of Performance than conventional absorption heat pumps by utilization of a substantially saturated salt solution cycle between at least one pair of: (1) an absorber and generator, or (2) a condenser and evaporator, wherein the salt is crystallized to the solid phase in the generator or evaporator, respectively, and the heat of crystallization is utilized for refrigerant vaporization.
2. Description of the Prior Art
Absorption type air conditioning processes and apparatus have been known for providing cooling and heating for many years. However, the conventional absorption cycle has been recognized to have relatively low Coefficient of Performance for cooling and with the advent of higher efficiency gas fired furnace equipment, the Coefficient off Performance (COP) for heating of absorption-type heat pumps has also become only marginally better. Absorption air conditioners for cooling under optimized conditions represented by heat-source temperatures of about 200.degree. to about 350.degree. F. and heat-sink temperatures of about 85.degree. to about 115.degree. F. have demonstrated steady-state cooling COP of about 0.5 to about 0.7. Similarly, absorption heat pumps, currently under development and known to the present inventors, for heating under optimized conditions represented by heat-source temperatures in the generator of about 270.degree. to about 360.degree. F. and heat-sink temperatures in an outdoor coil of about 0.degree. to 40.degree. F., have demonstrated in the laboratory steady-state heating COP of about 1.1 to about 1.2. Commercial absorpition cooling systems have used water-lithium bromide and ammonia-water refrigerant-absorbent fluids. Developmental absorption heating systems have used ammonia-water and ETFE-R133A (a proprietary composition of Allied Chemical Corporation) as the working fluid. There have been attempts to improve the conventional cycle efficiency of absorption-type, gas-fired heat pumps including:
operation at high generator temperatures to take advantage of cascading effects, commonly called double-effect systems; evaporative cooling of the absorber of air-cooled salt-water systems; and development of new absorption fluid systems. None of these attempts known to the inventors have been satisfactory due to one or more of the following reasons: high temperature corrosion of common materials of construction and the need for costly materials; undesired complexity of the process and apparatus; and only slightly superior performance coupled with the thermal and chemical instability of the fluid systems.
Prior art absorption refrigeration systems are well known as exemplified by U.S. Pat. No. 3,620,036 teaching that solidification or crystallization of the absorbent solution in an absorption refrigerations system should be avoided. U.S. Pat. No. 3,054,272 teaches an absorption refrigeration system using a saline solution as an absorbent and a refrigerant miscible therein, the capacity being adjusted by precipitating salt in the generator to decrease the capacity and permitting the solution to absorb precipitated salt to increase the system capacity. U.S. Pat. No. 2,986,525 teaches use of solids, such as lithium or ammonium nitrates and chlorides as absorbents for refrigerant gases in the generator of absorption refrigeration apparatus. Eutectoid particles form a solid, porous body which substantially fills the generator and absorbs about one half of its weight of ammonia charging the generator. The charged generator may then be incorporated into a refrigeration system and the discharge and absorption of gaseous ammonia cycled for the refrigeration cycle. U.S. Pat. No. 3,717,007 teaches an air-cooled double-effect salt solution absorption refrigeration system having high and low pressure generator stages utilizing an absorbent more dilute in salt content than absorbents normally employed to avoid formation of crystals. Other recent U.S. patents relating to absorption refrigeration systems include U.S. Pat. Nos. 4,014,183; 4,085,596; 4,171,619; 4,223,539 and 4,269,034.